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Tapestry Woven From Organic Threads

Materials Chemistry: Interlaced covalent organic framework with reversible elasticity could lead to thin films, electronic devices

by Stu Borman
January 25, 2016 | A version of this story appeared in Volume 94, Issue 4

Synthesis of an interlaced covalent organic framework.
Credit: Science/Courtesy of Enrique Gutierrez-Puebla
Benzidines (black) are added to the ends of copper bisphenanthrolines. A condensation reaction then links the bisphenanthrolines to form a woven material (right).

In an extension of chemical domesticity, researchers have shown that organic chemistry is good not only for cooking but for weaving as well. Several types of supramolecular structures—catenanes, rotaxanes, molecular knots, and molecular Borromean rings—have interwoven two- and three-dimensional parts. Now, Osamu Terasaki of Stockholm University; Omar M. Yaghi of the University of California, Berkeley; and coworkers have designed and constructed the first structures in which 1-D molecular “threads” are interwoven, forming a crystalline covalent organic framework (Science 2016, DOI: 10.1126/science.aad4011). The researchers first synthesized a copper(I) bisphenanthroline complex in which the two organic groups adopt an interlaced inverted-U orientation. They then added benzidines to the ends of the organic groups and linked the benzidines by forming imine bonds, creating a woven material they call COF-505. The copper ions can be removed and reinserted reversibly. The demetalation increases the material’s elasticity 10-fold because the threads can move around more easily without copper present. The material could be used for preparing controllably flexible thin films and electronic devices. “Interweaving organic threads in the solid state is totally new and will lead to unexplored materials with unexpected properties,” comments Jean-Pierre Sauvage of the University of Strasbourg.


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